Toroidal core electrical transformer with cooling fins



Il sn INVENTOR ATTORNEY 5 Sheets-Sheet 1 A. A. HALACSY March 29, 1966lTOROIDAL CORE ELECTRICAL TRANSFORMER WITH COOLING FINS Filed Aug. 5.1960 FIG. 2

A, A. HALACSY TOROIDAL CORE ELECTRICAL TRANSFORMER WITH COOLING FINSMarch 29, 1966 5 Sheets-sheet 2 I Filed Aug# 19Go INVENTOR ANDREW A. HALACSY www ATTORNEY March 29, 1966 A. A. HALAcsY 3,243,744

TOROIDAL CORE ELECTRICAL TRANSFORMER WITH COOLING FINS Filed Aug. 5.1960 5 Sheets-Sheet 5 INVENTOR ANDREW A. HALACSY ATTORNY March 2 9, 1966A, A, HALACSY 3,243,744

TOROIDAL CORE ELECTRICAL TRANSFORMER WITH COOLING FINS Filed Aug. 3.1960 5 Sheets-Sheet 4 INVENTOR. arew ,4. /a/acsy A TTORNEY March 29,1966 A, A, HALACSY 3,243,744

TOROIDAL CORE ELECTRICAL TRANSFORMER WITH COOLING FINS Filed Aug. 5.1960 5 Sheets-Sheet 5 11a FIG" H6 y 1M .f--r 'T'-Y Ig--Li M M2004) 4FIC-3.12

M Il :130 illltllllbllill o: INVENTOR.

drew A. Halacsy BY fj S- @Mg y,4 TTaRA/EY United States Patent O3,243,744 TORGIDAI. CURE ELECTRICAL TRANSFRMER WI'II-I COGLING FINS 4Andrew A. Halacsy, Elizabeth, NJ., assignor to Federal Pacific ElectricCompany, a corporation of Delaware Filed Aug. 3, 1960, Ser. No. 47,201 6Claims. (Cl. 336-61) This invention relates generally to an electricaltransformer and more particularly to a new construction thereofproviding improved cooling and mounting means.

The present invention applies especially to dry-type transformers oftoroidal configuration, but certain of its aspects `are not limitedthereto. In such transformers, the heat generated by the magnetic fluxin the core and the heat developed by the electrical current in thewindings, ows outward and is dissipated in the ambient atmosphere. Suchheat flow is accompanied by temperature rise in the insulation of thewindings. The temperature rise is an important limiting factor in theloading of the winding and limits the selection of insulation materialsusable therein to a relatively expensive group. More particularly, theheat generated in the inner winding combines with the heat generated inthe core and this cumulative heat quantity flows across the insulationbetween the inner and outer windings into the latter subjecting suchinsulation to a heat rise corresponding to this cumulative effect.Similarly the heat generated in the outer winding adds to the heatgenerated in the core and the inner winding and this heat quantitysubjects the insulation surrounding the outer winding to a correspondingheat rise. The temperature differential between the core and outersurface of the transformer approximately corresponds to the sum of thetemperature increase across the insulating layers (the temperaturedifference across the windings is neglected) and one important object ofthe present invention is to obtain a substantial reduction in thistemperature differential so that a transformer with a given insulationmay be more hreavily loaded or, for a given loading, a lower costinsulation may be used. Pursuant to this object of the present inventiona novel arrangement is provided for dissipating heat from between thewindings and/ or between the core and inner winding to the ambientatmosphere, resulting in a cooler operating transformer having theattendant advantages aforenoted. Accordingly, the present inventionpaves the way for higher rated dry-type transformers than was heretoforepossible.

Yet another object of the present invention is the provision of agenerally improved electrical transformer of novel and economical designand construction which is particularly well-suited to dissipating heatresulting from inherent losses within the transformer and which iseminently suitable for its intended purpose.

Another important object of the present invention is the provision of anarrangement for mechanically protecting the transformer and itscomponents in storage and while being transported. A related featureresides in novel transformer structure effective for facilitating themobility and transporting of the transformer.

In an illustrative embodiment of the present invention in its variousaspects, a toroidal transformer is provided with a plurality of coolingtins in a novel arrangement relative to the windings. Additionally oneform of the illustrative transformers is provided with novel coaxialrings spaced apart so as to generate an imaginary protective cylinderfor the transformer. As a further feature, the terminal bushings thatproject from the illustrative encapsulated coil body are disposed withina protected space. A further specific feature of the invention residesin the integration of the aforementioned transporting and protectiverings with cooling iins projecting from ICC the transformer body. Astill further feature resides in forming the rings in a manner toreceive a rope, or the like, to facilitate handling and installation ofthe transformer.

A further feature of the invention resides in the provision of adouble-ended transformer having the primary high-voltage terminals atone end and the low-voltage terminals at the opposite end. Suchtransformer structure is suitable for mounting with the high-voltagetermiA nals at the top and readily accessible for connection toover-head power lines and with the low-voltage secondary terminals atthe bottom, accessible for the low voltage connection.

Yet another object of the present invention is the provision of adry-type distribution power transformer of generally improved designedand construction.

Other features, objects, and advantages of the present invention willbecome apparent as the description thereof proceeds when considered inconnection with the accompanying illustrative drawings in which:

FIGURE l is a fragmentary plan View of a transformer embodying featuresof the present invention;

FIGURE 2 is a vertical sectional View taken along the line 2-2 of FIGUREl;

FIGURE 3 is a side elevational View of a modified form of cooling iin;

FIGURE 4 is a sectional View taken on the line 4-4 of FIGURE 3;

FIGURE 5 is a view similar to FIGURE 1 showing a modified form oftransformer cooling arrangement;

FIGURE 6 is a vertical sectional view taken along the line 6-6 of FIGURE5;

FIGURE 7 is a plan view of a ring and cooling iin casting unit, utilizedin pairs in the embodiments of FIG- URES 5 and 6;

FIGURE S is a fragmentary View showing still another modified form oftransformer cooling arrangement, said view being shown in horizontalsection;

FIGURE 9 is a plan view of yet another embodiment of the invention incertain of its aspects;

FIGURE 10 is a section view taken along the line X-X of FIGURE 9 showingthe general construction of a transformer fabricated `according to theteachings of the present invention;

FIGURE 1l is an enlarged fragmentary sectional view showing a terminaland bushing of the primary winding in the transformer of FIGURES 9 andl0 connected to a plug-in connector illustrated in phantom; and

FIGURE l2 is a View showing mounting of the transformers hereinbeforedescribed.

Referring to the drawings, and more particularly to FIGURES l-4 thereof,there is shown a dry-type electrical transformer l0 of toroidalconfiguration characterized by the improved cooling and mountingarrangement to be described in detail below. The transformer comprises acore 12 of any suitable design and construction and formed of anysuitable magnetic material, such as silicon steel. In the illustratedembodiments, the core 12 is formed of strip stock wound to form stackedlayers of laminations and to assume an overall annular or toroidalconfiguration. The groups of layers are of overall reduced width atincrements spaced from the center of the core so that the latter may beof the generally circular cross-section shown in FIGURE 2. Surroundingthe core are spaced layers 14, 16, 18 and 20 of insulation, the innerwinding which is composed of two spaced layers 22 and 22a, and the outersingle layer winding 24. The inner winding layers 22 and 22a aredisposed between the insulation layers 14 and I6, and 16 and I8,respectively, Whereas the outer winding layer 24 surrounds insulationlayer 18. Either winding may be the high-voltage winding with the otherbeing the lowvoltage winding. The high voltage winding is the innerwinding of the illustrate embodiment.

Pursuant to certain aspects of the present invention, the temperaturedifferential between the core and the outer surface of the transformeris substantially reduced, there being provided an arrangement fordissipating heat from between the windings and/ or between the core andinner winding. More particularly, there is provided a series ofuniformly spaced radially extending cooling fins 26 (FIGURES 3 and 4)which may be formed of any suitable non-magnetic material having goodthermal conduction properties, such as aluminum. The cooling finsconduct the heat, from the heat path defined between the inner and outerwindings, to the ambient atmosphere. Each cooling fin 26 comprises aninner arcuate part or extension 28 which is disposed in the heat pathbetween the inner and outer windings. Inner part 28 conforms to theconfiguration of the windings and extends transversely substantially tothe adjacent cooling fin 26. In a longitudinal peripherally extendingdirection between terminal points 38 and 32, the part 28 extends forapproximately 180 degrees of the core and windings, as best shown inFIGURE 2. Extending, substantially at right angles, from part 28 is aweb 34 which conducts the heat from part 28 through the outer winding tothe ambient atmosphere. The web or part 34 presents a substantialsurface area to the atmosphere for the heat dissipating function. Web 34is of plate-like construction and may be corrugated as indicated at 36for increasing the surface area and strengthening. The web 34 enlargesin area from arcuate part 28 to the opposite edges 38, there beingdefined the opposite diagonal edges 40 between edges 38 and inner edges42. The outer edge of cooling fin 26 is defined by edge 44. A pair ofsmall apertures 46 are disposed in the region of points 30 and 32 for apurpose which will be apparent from the description which follows.

A series of convolutions of the winding layer 24 extend around part 28and aid in retaining the individual cooling fins 26 in position. Suchfins are collectively retained in assembled relation, to form a framefor the transformer by binding wires 48 which extend through a companionseries of apertures 46 and by the external assembly rings t). Moreparticularly, one binding wire 48 extends through one series ofapertures 46 at one diametrical position of the body of the transformerand the other binding wire 48 extends through the other series ofapertures 46 at the opposite diametrical position. The rings 50 arelaterally spaced at the opposite ends of the tins and surround thelatter, said rings having inner surfaces 52 and 54 which are welded tothe edges 38 and 44, respectively of the fins. In this manner the rings50 are rigidly united to form a supporting frame for the transformer.

It will be understood that the parts 28 of the fins collectively form asurface area of substantial proportions blanketing approximatelyone-half the heat path defined between the inner and outer windings. Theheat dissipating surface area of the fins substantially increases awayfrom the body of the transformer to effectively dissipate the heatconducted along the fins to the ambient atmosphere. The heat generatedin the core and inner winding, instead of streaming into the outerwinding, streams into parts 28 and is dissipated to the atmosphere bythe fin parts 34. Thus this heat will not traverse the insulation of theouter winding.

It may be observed that the heat transfer portions 28 are in extendedarea opposition to only the outer half of each turn. Resistance heatingoccurs throughout the whole turn. This suggests the possibility ofinadequate dissipation of the heat that develops in the inside halfturnsand the corresponding possibility of an excessive temperature rise inthe inside half-turns. However, this does not occur. The heat developedin the inside halfl4 turns is effectively transferred by conductionalong the turn itself (being a good heat conductor such as copper oraluminum) to the outer-half turn where it is dissipated by transfer tothe aforementioned cooling fin assembly.

The insulation is traversed by only a portion of the heat generated inthe outer winding because only a portion of such heat will flow inwardlyinto the parts 28 of the fins. Parts 28 are disposed between theinsulation layers 18 and 2t) as shown in FIGURE 2. The radiallyextending spaced fins define grooves for the winding of the outer layer24, said grooves guiding the winding operation and also serving assupports for said layer thus increasing the short circuit strengththereof. The space S defined between the core and insulation layer 14may be filled with sand or any other suitable material. The completedtransformer is encapsulated, as shown in FIG- URE 10, by a technique notforming a part of the present disclosure.

Referring to FIGURES 5-7, there is shown another transformer which issimilar to the above described embodiment and differs t'herefrom in therespects to be pointed out in detail below. Parts of transformer 10corresponding to transformer 10 are denoted by the same referencecharacters primed. In transformer l0 the cooling fins 26 and assemblyrings 50 are formed as integrally cast units rather than individualunits to facilitate manufacture and assembly, the cooling finsfunctioning in themanner aforedescribed. The cooling fins and assemblyrings are lformed as a pair of cast units (FIGURE 7) which are suitablyunited along the diametrical parting line 62 over the inner winding.Each unit thus consists of one-half the requisite number of fins 26 `andone-half the circumferential extent of the rings 50. The assembled units60 define a peripherally continuous arcuate part 28, which correspondscollectively to parts 28 previously described, the part 28' beingdisposed in the heat path between the inner and outer windings andextending for approximately 180 degrees thereof. Extending from part 28are fin parts or webs 34', which conduct the heat from the core andinner winding yand part of the heat of the outer winding to theatmosphere. Thus the problem of individual cooling n orientation andassembly are eliminated pursuant to the instant embodiment 10 whichretains all of the functional advantages aforenoted. It will beunderstood that the cooling fins and assembly rings may be formedindividually and suitably united or formed as a plurality of sectionalunits united by welding, or in any other suitable manner.

Wit'h reference to FIGURE 8, there is shown another transformer 10 whichis generally similar to the previous embodiments, differing therefrom inthe respects now to be described, the same parts being designatedl bythe same number double primed. In transformer 10" cooling fins extend inthe heat path defined between the core 12 and inner winding 78 as wellas in the heat path defined between the inner winding and outer winding72, so that there is a resulting heat transfer from the core and windingindependent of each other to further reduce the operating temperature ofthe transformer. Extending around the core .and windings are 4theinsulation layers 74, 76, 78, and 82. The cooling fins extending in theheat path between the core and inner winding correspond to thearrangement of transformer 10', i.e., the cooling fins 84 are parts ofintegrally cast units 86 united as aforedescribed. More particularly,the fins 84 have a peripherally continuous arcuate part S8 disposed insaid heat path, the heat from the latter being conducted from part 88 tothe ns for dissipation in the atmosphere. The cast units 86 are shownwithout rings 50', it being understood that such rings may be provided,if desired.

Disposed between each pair of adjacent fins 84 is an individual coolingfin 90 for conducting heat from the heat path between the inner andouter windings to the atmosphere. Each winding fin 90 includes anarcuate part 92 which extends `in the heat path between the inner andouter windings for conductive heat therefrom along the fins fordissipation in the atmosphere. The cooling ns 90 thus are generallysimilar to the fins 26 of the transformer 10, the parts 92 of fins 90being symmetrically disposed with respect to the tins. It will be notedthat the parts 92 are spaced from each other to dene a passage 94 forthe extension therethrough of the fins 84. The fins 84 extend to theambient atmosphere between convolutions of the inner and outer windings,and the fins'90 extend to the ambient .atmosphere between convolutionsof the outer winding. In practice, the inner winding is wound around,part 8S, the ns 84 defining grooves for the winding operation. The outerwinding is wound around parts 92 to retain the fins 90 in position. Heatgenerated from the core and inner winding 'is conducted to theatmosphere -by fins 84 and heat generated from the inner and outerwindings is conducted to the atmosphere by tins 90 as indicated by lthearrows.

Referring to FIGURES 9 through 1l there is shown still anotherembodiment of the transformer which is similar to the above describedembodiments and differs therefrom in the respects to be pointed out indetail below. Parts of'transformer 10 corresponding to transformer 10are denoted by the same reference characters triple primed. Thetransformer comprises a toroidal core 12 of lany suitable design andconstruction and formed of any suitable magnetic material, suc'h assilicon steel. Surrounding the core are spaced layers 14', 16', 18"',and 20 of insulation, the inner winding which is composed of two spacedlayers 22" and 22a'", and the outer single winding layer 24"'. The innerwinding layers 22" and 22a' are disposed between the insulation layers14"' an-d 16', and 16" and 18', respectively, whereas the outer windinglayer 24 surrounds insulation layer 18". At least layer 18 is formed asa cast-insitu unitary and continuous polymerized covering, additional toany insulation on the individual turns of wire. 'The highvoltage windingis the inner winding of the illustrated embodiment. The space betweenthe core and layer 14' of insulation is filled with a suitable fillermaterial S" such as sand.

' The inner winding is `formed by the continuously wound conductor 100having formed plug-in terminals 102 and 104 at the opposite ends thereoflaterally encased within the projecting bushings 106 and 108,respectively. Said bushings have integral circular ribs, as shown, andare formed of plastic insulating material or encapsulant as acontinuation of the encapsulating layer 110 o-f the conductor 100. Moreparticularly, the encapsulation 110 about the high-voltage leads 100 andterminals 102 and 104 extends continuously from the continuousuninterrupted encapsulating layer 112 which covers the winding 24 toeffectively shield this winding and its terminals against outsideinuences, such as moisture, chemical contaminants, etc. A preferredmaterial for this purpose is silicon rubber bemause of its excellentinsulation resistance, its ability to withstand high temperatures, itsflexibility, and its adaptability of the casting procedure such as hereinvolved.

The bushings and terminals of the high-voltage winding are xed inposition at one side of the transformer unit 10" by being imbedded inthe filler material 114, said bushings and terminals projecting beyondthe transformer body. The material 114 which iills the body space of thetransformer is selected from su-itable materials such as epoxy resin andthe like and is positioned by known methods such as casting. Theterminals are adapted for plug-in connection with a complementary maleplug-in type connector 116 (FIGURE 1l) of any well-known type, at theend of a cable 118.

Projecting at the opposite sides of the transformer unit 10" arelow-voltage terminals 120 of the outer windings, the latter being formedin two sections with a pair of terminals 120 for each section. Theterminals 120 are fixed in position by the cast filler 114 in the mannerof bushings 102, 104. The terminals are suitably secured to the properconductors 122 of the outer windings, as by brazing or welding. Themethod of forming the inner winding has been described heretofore, itbeing understood that either or both windings may be formed in likemanner. After the transformer has been assembled as hereinbeforedescribed, a molding operation may be carried out in any well-knownmanner to encapsulate the transformer conductors and terminals so as toform an integral unit such as by spraying or dipping in known materialssuch as silicone rubber.

Referring once again to FIGURES 9 through l2, another feature of thepresent invention relates to the protection of the transformer and itscomponents in storage or transport and for providing for the readymobility and maneuverability thereof. The rings 50 have a common axiscoincident with the axis of the core, said rings generating an imaginaryprotective envelope for the transformer and its projecting components,including bushings 106, 108 and the low-voltage terminals 120. Moreparticularly, the fins 26" are of diverging configuration away from thecore and extend laterally of the transformer beyond the projectingcomponents 106, 108, 120 thereof, the rings 50 being disposed at theends of the tins laterally beyond said projecting components. Expresseddifferently, the outer peripheral edges 124 of the rings are disposed ina plane laterally beyond the plane of the projecting components so as toprotect the latter when the transformer is supported on its side or whenother apparatus or materials are stacked thereon. This lateraldisposition of the rings also protects the projecting components duringthe transporting or maneuvering of the transformer thereon. Thetransformer is readily moved or transported on the rings 50' which serveas wheels for rolling the transformer, the rings being radiallyoutermost of the transformer. The external arcuate edge 126 of the ringsdefine the rolling edges thereof and the imaginary cylinder generatedbetween such edges defines a protective peripheral enclosure for thetransformer 10".

Laterally adjacent to edges 126, inboard thereof, are peripherallyextending grooves 128 which are adapted to receive a rope or chain whichis trained around the rings to facilitate maneuvering of the transformerunit. Close control can thus be achieved in the handling of the unit bymeans of ropes, or the like, trained around the rings in grooves 128.

From the above it will be apparent that the rings on which thetransformer unit may be facilely rolled or maneuvered generates animaginary protective envelope for the transformer and its projectingbushings terminals, said rings being radially and laterally outermost ofthe unit.

Referring more particularly to FIGURE l2 therein may be seen how thetransformer 10 is adapted to be mounted by standard clips 130 to thedistribution pole 132. The clips are bolted to the transformer at pointsconvenient therefor before or after the clips are secured to the pole.In the drawing it may be seen that the transformer is mounted with thehigh-voltage bushings 102, 104 uppermost, thus being convenientlylocated for attachment of the high-voltage lines 134 thereto. Inaddition the low-voltage connections are made beneath the transformer,so that these service wires 136 may be easily drawn therefrom.

Double ended construction of power transformers is novel and results inthe attainment of hitherto unattainable advantages. As for example, atransformer fabricated according to the teachings of the presentinvention produces a separation between the high-voltage and lowvoltagelines not possible before without additional expensive structure.Additionally, it simplifies the installation of the transformer, andincreases the safety of the installing and maintaining personnel. Theopen con- 7 struction of the transformer produces a self-cleansingeffect when subjected to natural rainfall.

Various additional modifications of the above described embodiments ofthe invention will readily occur to those skilled in the art, andtherefore the invention should be broadly construed in accordance withits full spirit and scope.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. An electrical transformer comprising a toroidal magnetic core andheat generating windings thereon arranged as inner and outer layers ofcurrent-carrying convolutions having layers of insulation between thelayers of convolutions, said magnetic core being of circular crosssection as viewed in a plane containing the toroidal axis, and means forconducting heat to the ambient atmosphere comprising a series of heatconducting members each having a first metal portion extending along thecore locally and confronting at least one of said layers ofconvolutions, said first metal portions being of semicircular crosssection and disposed to confront the peripherally outward portion ofsaid toroidal core, said members each having another metal portionextending integrally from said first portion and disposed radiallyoutward so as to extend between adjacent convolutions of at least one ofsaid layers into the ambient atmosphere.

2. An electrical transformer comprising a magnetic core of toroidalconfiguration having a heat generating winding thereon, and a series ofarcuately spaced metal cooling fins extending generally radially fromsaid winding to the ambient atmosphere, said fins having portionsextending to the interior of said winding and being in intimate heattransfer relationship therewith, said cooling fins also havingsubstantial areas, respectively, exposed to the ambient atmosphere,means interconnecting the radially outermost extremities of said coolingfins at points spaced axially so as to constitute a cylindricalstructure having an axis coincident with the axis of said core anddefining a rolling surface for the transformer.

3. An electrical transformer comprising a toroidal core and heatgenerating windings extending therearound disposed as inner and outerlayers of current carrying convolutions and layers of insulation betweensaid layers of convolutions, and means for conducting heat to theambient atmosphere comprising a first series of heat conducting memberseach having a first portion extending locally along the core anddisposed between said core and the innermost layer of said convolutionsand each having another portion integral with said first portion andextending radially outward between convolutions of all said layers andthrough said layers of insulation, and a second series of heatconducting members each having a first portion extending locally alongthe core between inner and outer layers of said convolutions and saidsecond members each having another portion integral therewith anddisposed to extend radially outward between convolutions of said outerlayer, the radially extending portions of said second series of heatconducting members being interspersed with the radially extendingportions of said first series of heat` conducting members and theradially extending portions of both said series projecting into theambient atmosphere and having a substantial area exposed thereto.

4. An electrical transformer comprising a toroidal magnetic core andheat generating windings thereon arranged as inner and outer layers ofcurrent-carrying convolutions having layers of insulation between thelayers of convolutions, and means for conducting heat to the ambientatmosphere comprising a series of heat conducting members each having afirst metal portion extending along the core locally and confronting atleast one of said layers of convolutions, said first metal portionsbeing integrally connected and extending half-way around the axis of thetoroidal core, said members each having another metal portion extendingintegrally from said first portion and disposed radially outward so asto extend between adjacent convolutions of at least one of said layersinto the ambient atmosphere.

5. An electrical transformer in accordance with claim 3 furtherincluding a pair of rings of equal diameter coaxial with the axis of thetoroidal core, said rings being separated axially and being joined tothe outermost portions of both said series of heat conducting membersfor uniting said heat conducting members and defining a rolling surfacefor the transformer and `constituting mechanical protective meanstherefor.

6. An electrical transformer in accordance with claim 2, furtherincluding, electrical terminals connected to said winding, wherein saidinterconnecting means includes portions at the axial extremities of saidcooling fins in planes between which said core and said winding and saidterminals are disposed for providing protection against mechanicaldamage.

Gellert et al 336-96 X ROBERT K. SCHAEFER, Primary Examiner.

MILTON O. HIRSHFIELD, JOHN F. BURNS,

Examiners.

E. E. NORRIS, W. M. ASBURY, E. JAMES SAX,

Assistant Examiners.

1. AN ELECTRICAL TRANSFORMER COMPRISING A TOROIDAL MAGNETIC CORE ANDHEAT GENERATING WINDINGS THEREON ARRANGED AS INNER AND OUTER LAYERS OFCURRENT-CARRYING CONVOLUTIONS HAVING LAYERS OF INSULATION BETWEEN THELAYERS OF CONVOLUTIONS, SAID MAGNETIC CORE BEING OF CIRCULAR CROSSSECTION AS VIEWED IN A PLANE CONTAINING THE TOROIDAL AXIS, AND MEANS FORCONDUCTING HEAT TO THE AMBIENT ATMOSPHERE COMPRISING A SERIES OF HEATCONDUCTING MEMBERS EACH HAVING A FIRST METAL PORTION EXTENDING ALONG THECORE LOCALLY AND CONFRONTING AT LEAST ONE OF SAID LAYERS OFCONVOLUTIONS, SAID FIRST METAL PORTIONS BEING OF SEMICIRCULAR CROSSSECTION AND DISPOSED TO CONFRONT THE PERIPHERALLY OUTWARD PORTION OFSAID TOROIDAL CORE, AND MEMBERS EACH HAVING ANOTHER METAL PORTIONEXTENDING INTEGRALLY FROM SAID FIRST PORTION AND DISPOSED RADIALLYOUTWARD SO AS TO EXTEND BETWEEN ADJACENT CONVOLUTIONS OF AT LEAST ONE OFSAID LAYERS INTO THE AMBIENT ATMOSPHERE.